Evolution of correlated characters

1
Evolution of correlated characters selection
acts on individuals, not traits few traits are
completely independent e.g., forelimbs
and hindlimbs similar developmental pathways,
similar genes e.g., size of red shoulder
patch on a Red-Winged Blackbird pigment
precursor may be involved in multiple biochemica
l pathways pleiotropy (one gene, many
traits) polygeny (many genes, one trait)
---gt many loci, many traits
genetic correlations
2
linkage disequilibrium can produce genetic
correlations locus A only affects trait z1,
locus B only affects trait z2
D 0 D 0.15 D -0.15
no positive negative
correlation correlation correlation
3
pleiotropy can produce genetic correlations locus
A (with additive alleles) affects both trait z1
and z2 phenotypic correlations may also
arise from environmental effects
rG and rE positive rG no
rG both positive negative rE
negative rE
4
Model for quantitative trait evolution single
trait R h2s amount of phenotypic change
(R), depends on amount of VA (h2)
and strength of selection (s) several
traits Dz GP-1s z is the trait
vector (z1 z2 z3 zn) Gb s is
still selection differential (z zs) G,
P are the genotypic and phenotypic variance-c
ovariance matrices b is the selection
gradient si 3 Pijbij Pi1b1
Pi2b2 Pi3b3 Pinbn direct
indirect b1 is the partial regression
coefficient
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An extended derivation, for those who want
it Dz G P-1 s genotypic phenotypic
(
(
(
(
)
)
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)
-1
DzA s2A covAB s2A covAB sA DzB covBA
s2B covBA s2B sB

(
)
1 s2B -
covAB (s2A)(s2B) (covAB)(covBA) - covBA
s2A
P-1
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(No Transcript)
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Directional natural selection on Geospiza fortis
in 1976-77 and 1984-86. standardized
selection coefficients differential
gradient s b SE 1976-77 (n632)
weight 0.74 0.477 0.146
wing length 0.72 0.436 0.126
tarsus length 0.43 0.005 0.110
bill length 0.54 -0.144 0.174
bill depth 0.63 0.528
0.214 bill width 0.53
-0.450 0.197 1984-86 (n549) weight
-0.11 -0.040 0.101 wing length
-0.08 -0.015 0.084 tarsus length
-0.09 -0.047 0.076 bill length
-0.03 0.245 0.095 bill depth
-0.16 -0.135 0.136 bill
width -0.17 -0.152 0.125 Grant
Grant 1995 Evolution 49241
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Evolutionary genetics of feeding
behavior in the garter snake,
Thamnophis elegans two
populations coastal -- eat slugs inland --
no slugs occur eats fish and aquatic amphibians
(Arnold 1981)
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feeding response to slugs is influenced by genes
coastal eat slugs inland avoid slugs
10
Genetic correlations between responses to
different prey odors in two populations of
Thamnophis elegans Hyla Batrachoseps
Taricha fish slug
leech Hyla --- 1.10 -0.24
0.18 0.88 1.01 Batrachoseps 0.81
--- 0.07 1.00 1.34
0.98 Taricha -0.45 0.57 --- 0.09
-0.55 -0.88 fish 0.89 1.27
0.02 --- 0.59 0.84 slug -0.03
0.56 -0.79 0.19 ---
0.89 leech 0.07 0.77
-0.01 -0.38 0.89 --- coastal above
diagonal inland below diagonal
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Response to leeches (risk)
avoid accept
avoid accept
Response to slugs (food)
12
L
Response to leeches (risk)
avoid accept
H
avoid accept
Response to slugs (food)
13
Selection against eating leeches is stronger than
selection for eating slugs (slugs are rare)
L
Response to leeches (risk)
avoid accept
H
avoid accept
Response to slugs (food)
14
Selection for eating slugs is stronger than
selection against eating leeches (slugs are
common)
L
Response to leeches (risk)
avoid accept
H
avoid accept
Response to slugs (food)